<!DOCTYPE html>
<html>
<head>
 <title>计算器</title>
 <meta charset="utf-8" />
</head>

<body>
 <input id="num1" />*<input id="num2" />
 <button onclick="jiSuan()" /> =</button> 
<input id="num3" />


<script>

function jiSuan(){
num3.value=num1.value*num2.value;
}
</script>

</body>
</html>